Conventional methods of fabricating silicon on insulator (SOI) substrates, such as subjecting silicon wafers to oxygen ion implantation or oxygen plasmas suffer from relatively high defect levels in the buried oxide (BOX) layer so formed. Additionally, for some applications the buried oxide layer inhibits optimum operation of devices formed in the silicon layer. Therefore, there is a need for improved methods of forming buried isolation regions in semiconductor substrates and for methods of forming semiconductor devices with buried isolation and still provide optimum operation of the devices.